Linear position sensor using a strain gage

Abstract

A linear position sensor for sensing the position of an attached object. The linear position sensor uses a strain gage to detect the position of the object. The sensor includes a housing and a ramp shaped actuator located in the housing. The actuator is attachable to the object. A strain gage is positioned in contact with the actuator. The actuator applies a strain to the strain gage as the actuator is moved. The strain gage generates an electrical signal that is proportional to the position of the object.

Description

1. Field of the InventionThis invention pertains to position sensors which are both durable and precise for application in rugged and demanding environments, particularly for application with internal combustion engines.2. Description of the Prior ArtThere are a variety of known techniques for position sensing. Optical, resistive, electrical, electrostatic and magnetic fields are all used with apparatus to measure position. There are many known apparatus for using these energies for sensing. A few of the known apparatus are resistive contacting sensors, inductively coupled ratio detectors, variable reluctance devices, capacitively coupled ratio detectors, optical detectors using the Faraday effect, photo-activated ratio detectors, radio wave directional comparators, and electrostatic ratio detectors. There are many other known detectors, too numerous to mention herein.These detection methods tend to each offer much value for one or more applications, but none meet all application re...

AI Technical Summary

Problems solved by technology

These detection methods tend to each offer much value for one or more applications, but none meet all application requirements for all position sensing applications.

The limitations may be due to cost, sensitivity to particular energies and fields, resistance to contamination and environment, stability, ruggedness, linearity, precision, or other similar factors.

Transportation applications generally, and specifically automotive applications, are very demanding.

Temperatures may rise to 150 degrees Centigrade or more, with road contaminants such as salt and dirt splashing upon the engine compartment.

This may occur while the engine is still extremely hot from operation.

However, the resistive position sensors are not without limitations.

However, magnetic position sensors have issues with linearity and maintaining tolerances.

Regardless of the arrangement and method for changing the field about the sensor, the magnetic circuit faces several obstacles which degrade the performance of magnetic position sensors.

Since this will not be detected by the sensor, the sensor will provide a reading of insufficient magnitude.

Failure to do so will result in unpredictable magnet performance.

However, operating at complete saturation leads to another problem referred to in the trade as irreversible loss.

Temperature cycling, particularly to elevated temperatures, permanently decreases the magnetic output.

Another significant challenge in the design of magnetic circuits is the sensitivity of the circuit to surrounding ferromagnetic objects.

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